Give the cards an edge again — one grey, not ten hues

The border was never the problem; a border that carried COLOUR was. It said
exactly what the fill already said, at 1.56-2.09 against that fill where the
fill managed 1.03-1.05 against the board — the loudest element on every card
was redundant with the quietest. A line that varies by colour is content and
competes with the fill. A line that never varies is structure and does not.

So the edge comes back, and it comes back as a constant in NoteCard rather
than a column in the palette. Uniformity is the feature, and putting it where
the palette cannot reach it is how that stays true.

  light  #b8b8b8    1.57-1.98 against all twenty card fills
  dark   #404040    1.58-1.73

Matched, not eyeballed: both land at ~1.6-1.7 against the card they edge, so
the edge reads with the same authority in either theme. Dark is `neutral-700`
— what the `default` card's border always was, one entry's value promoted to
the rule for all of them. Light sits between `neutral-300` and `neutral-400`
because neither lands in range: 300 fades to 1.18 on a gray-tagged card, 400
jumps to 2.52 and reads as a wireframe.

Rejected on measurement: a translucent black/white edge, which is the tidier
way to write it and self-adjusts per card. A border composites over the
card's own fill, so `border-white/20` comes out #56396d on a purple card and
#a3c9c1 on a teal one. Hue-coded edges are the thing being removed.

The shadow steps back to what it was for — depth, not the boundary. Web
returns to `shadow-sm`; Android's 2dp drops to 1dp, matching it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/notes/colors.ts

@@ -19,19 +19,20 @@ export type NoteColor = (typeof NOTE_COLOR_KEYS)[number];
 
 // The SUBDUED ramp — what a note wears when nothing chose a colour for it.
 //
-// NO BORDER, here or in the strong ramp below. A note card used to carry a 1px
-// `border-{hue}-900`, and measured against its own fill that line was a 1.56–2.09
-// contrast while the fill managed only 1.03–1.05 against the board. The loudest
-// thing on every card was therefore an identical line in an identical place, and a
-// board of them read as a grid of outlined rectangles no matter what colour was
-// inside — "too samey even with the color differences". The card's boundary now
-// comes from its fill in dark mode and from `shadow` in light (NoteCard.vue), both
-// of which vary with the card instead of framing it.
+// NO BORDER IN EITHER RAMP, here or below — the note card still HAS an edge, but it
+// is one grey for every card and it lives in NoteCard.vue, not in the palette. That
+// separation is the fix. The border used to be `border-{hue}-900` and measured
+// 1.56–2.09 against its own fill while the fill managed only 1.03–1.05 against the
+// board, so the loudest thing on every card was a line that said exactly what the
+// fill already said — and a field of them read as a grid of outlines however
+// different the colours inside were. A line that varies by colour is content; a line
+// that never varies is structure. Only one of those competes with the fill.
 //
 // The dark values are COMPOSITED HEX rather than a Tailwind step, and that is the
 // whole idea. `dark:bg-red-950/25` laid a hue over the near-black BOARD, which put
-// the card at the board's own lightness (1.03) — invisible without the border it
-// has just lost. These lay the same hue over the CARD SURFACE (`neutral-900`,
+// the card at the board's own lightness (1.03), which is why the old hue border had
+// to shout to be seen at all. These lay the same hue over the CARD SURFACE
+// (`neutral-900`,
 // #171717) at 18%, so an untagged card sits exactly where the default white card
 // always sat (1.11–1.14 vs the board, against `bg-neutral-900`'s 1.10) while
 // carrying LESS colour than before: chroma 7–17 where the old ramp had 10–23.